International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

Computer experiments were carried out with a simulation model of alloy crystallization in this work. The model was preliminarily calibrated for alloys of the Al-Si system. The presence of a non-equilibrium eutectic in pre-eutectic alloys with a silicon content of 1.0% – 1.6% has been detected. The minimum cooling rates at which the formation of an eutectic in these alloys is possible have been determined.

In this paper the physical model for high pressure water atomization of metal melts using hydraulic nozzle of a vortex type was proposed. The developed model assumes, that due to high speed water flow with significant centrifugal component of its velocity vector the rarefaction is formed, which causes intensive air suction leading to the formation of rotating gas (vapor-air) layer of toroid-like shape, providing a gap between the water flow and the metal stream. Thus water stream is separated from the heated surface of metal stream and the formation of particles during crystallization of melt droplets occurs due to surface tension mainly in this vapor-air layer. The cooling of melt droplets in the gas-water leads to the formation of spherical powder particles. The proposed model correlates well with the known experimental data on the production of spherical powders using a vortex-type annular hydraulic nozzle.

A study of a hypereutectic aluminum-silicon alloy AlSi18, modified by a conventional modifier – phosphorus (P) and a nanosized powder of a nanodiamond (ND) has been carried out. Refinement by 40.8% of the primary Si crystals and by 51% of the Si crystals in the composition of the eutectic has been obtained for the phosphorus-modified alloy in result of the modification. The refinement of the above values for the alloy modified by ND is 41.5% and 94% respectively. The phosphorus-modified alloy AlSi18 has an increased tensile strength (Rm) by 18.5%, relative elongation (А5) by 14.3% and hardness by 1.5%. The alloy, modiified by ND has an increased by 20.4% tensile strength (Rm), increased relative elongation (А5) by 7.15% and hardness decreases by 6.2%.

The results of studies of the regularities and mechanism of crystallization of polymer mixtures of high and low-density polyethylene in various proportions and composite materials based on blends of high and low density polyethylene taken in a 50/50 ratio are given. In filled composites, aluminum hydroxide was used in concentrations of 1, 3, 5, 10% wt. and bentonite in concentrations of 1, 3, 5, 10, 20, 30% wt. Dilatometric studies were carried out on an IIRT-1 device, in the process of stepwise cooling of samples with a load of 5.3 kg.

Mathematical models of crystallization of binary metal alloys crystallizing in the temperature range are proposed. These models are intended for use in the composition of quality control systems for cast alloys based on computer thermal analysis. The proposed models make it possible to calculate the time dependences of the relative amounts of the solid and liquid phases using the data of the cooling curve, as well as to determine the intensity of the increase of the amount of the solid phase. The method of determining the temperature dependences of the specific heat and latent crystallization heat using the data on the temperature-concentration dependences of the free energies of the phases forming the system under study was used.

A methodology was developed for the casting of samples of AlSi7Mg alloy modified with nanocomposites (NCs). The following NCs were used: SiC + Cu, AlN + Cu + Al, TiN + Cu, SiC + Al, SiC + Ag Cu, where Ag and Al are cladding metals. The introduction of the nanocompositions takes place in the crucible of a furnace. A thin-walled cylindrical casting mould is used on whose axis is installed a protected thermocouple to measure temperature variation as a function of time. The effect of NCs on overcooling and on sample structure is established.

The effect of a constant magnetic field during the crystallization of a hypereutectic aluminum alloy on its structure in the solid state investigated. It is shown that the superposition of the magnetic field positively affects the structure of the alloy. A uniform distribution of the doped phases and eutectic in the volume of the alloy is observed. The phase of primary silicon significantly changes the size and the shape. It is established that the influence of an external magnetic field reduces the dimensions of the shrinkage defects. In general, the effect of an external magnetic field on the structure of the alloy leads to an improvement in the operational properties. The obtained measurement results showed more stable hardness values over the cross section of the sample in comparison with the alloy that was not processed.

The influence of various factors on the processes of nonequilibrium crystallization of dipeptide (DPT) from its aqueous solutions has been studied. The nonequilibrium crystallization leads to the formation of spatially heterogeneous structures. Depending on the charge of the DPT molecule (neutral or anion), not only the morphology of the surface of the layers changes, but also its electronic structure. The important role is played by the properties of the substrate-layer interfaces, which are responsible for the formation of ferroelectrics on gold during the crystallization of the DPT anion. The structure of the solid layers is also significantly affected by charges on the substrate surface, which can partially or completely compensate for the charges of individual functional groups in the PT molecule. The observed effects of bipolar resistive switching in peptide layers and the formation of ferroelectrics can find practical application as a smart material of memristor organic lectronics.

A method is proposed for determining the temperature dependences of thermal effects (the amount of heat released when the temperature changes) based on data on the temperature-concentration dependences of the free energies of the phases of metallic systems. These dependences are necessary for modeling of the processes of crystallization of alloys. They make it possible to obtain temperature dependences of the dimensions of the thermal effects without introducing the results of measurements of direct calorimetry. The peculiarity of calculating of the temperature dependences of thermal effects upon cooling of binary metal systems from the liquid state to room temperature (including crystallization) is shown using the example of the alloy of the system Pb-Sn.

The basic principles of functioning of subsystems of the information-technological complex, which is intended for the forecast of structure and properties of the cast metal, are presented. The basis of subsystems are mathematical and simulation models of crystallization. The subsystem of thermal analysis is based on mathematical models, which were developed within the framework of the dynamic theory of metallic castings The subsystem of modeling of crystallization is based on a combination of mathematical models of heat conduction and diffusion with cellular automata. The model makes it possible to investigate in computational experiment the effect of various cooling conditions on the process of formation of the structure during crystallization. The results of computer experiment are shown.

Effective modification not by expensive nano-powders but by relatively large ones (up to several microns) and capable to dissolve when entering into the melt and become additional crystallization centers at its start point was shown. That provides a metal structure refinement and, consequently, increases the whole complex of mechanical properties. The optimal process parameters of refractory compounds disperse powders modification were proposed.

Obtaining gas-tight joints between mullite articles was made by crystallization of yttrium alumosilicate glass. The glass joint layer softens at joining temperature (1450-1470^oC) to bond the mullite samples without additional pressure and then crystallized during cooling. The good adhesion of crystallized glass to mullite surfaces ensue the gas-tight joints with permittivity 2.5*10^-4 sccm/cm. The eutectic like crystallization of initial yttrium aluminosilicate glass into yttrium silicate and mullite lead to formation the nanocomposite structure which ensure the 4 point bending strength value near 105 MPa.